''Active Directory is a feature within Windows 2000 that is designed to transform a disorganized vault of information, including individual user names, sites and passwords into an organized filing system that can be rearranged at will into various groups and domains as circumstances dictate.

In addition, Active Directory multiplies the filing system contents, replicating directory database information throughout all its locations, allowing one server to perform in lieu of another if a failure occurs.
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The three major characteristics are: 1) backbone network management system built into the operating system; 2) security management via internet protocols; 3) a platform for hosting other directory enabled functions

The implementation of ActiveDirectory require careful planning and use of highly skilled resources. The IT industry reported in 2003 that organizations started serious efforts in moving to this scheme only recently, and was triggered by end of support for the MicrosoftWindowsNt platform.

What do people who have banks of Linux servers use for DirectoryServices??

As ever, linux users have a lot of options. The best is probably LDAP, which is the basis of ActiveDirectory as well. The time-tested, mature solution is NIS , which stands for Network Information System and descends from Sun's yp (yellow pages) suite. Linux typically uses pluggable authentication modules, which means if you're willing to write a little code you can authenticate against virtually anything. Authentication modules exist for smart cards, relational databases and, to bring the discussion full circle, ActiveDirectory servers.

OpenLDAP is the LDAP implementation most often used in the Unix world. LDAP simply provides a hierarchical database. PAM (pluggable authentication modules) can be configured to perform authentications against LDAP directories. OpenLDAP includes utilities that can automatically synchronize LDAP trees between servers. Does that answer your question? I'm not sure what you're asking.